My first choice is Geno. He's acting like he's looking for the right way to act so that he's appears innocent, and heís all over the place.
The first two weeks he offered little aggressive sleuthing, mainly he just wanted to block someof the others. And this week, he was the most aggressive, and actually solved the riddle. He's all over the place and it's my suspicion that that's because he doesn't really know the best way to act so that he avoids suspicion.
But I like Dana as the killer too. She doesn't really try to find clues, she just dithers around, she doesn't want to play the allies vs allies games, and she rarely goes outside. I think she would sit in a lounge chair sipping sweet drinks if she could get away with it. Her knowledge of cyanide was impressive, but as a nurse and the daughter of a man who used it in his work (if that is true) she could legitimately have had that knowledge.
One thing we know was since the behind the scenes interviews were posted, the killer is as in the dark as everyone else, so no has special knowledge of the crimes, thus Dana's Cyanide insight doesn't really mean anything.
I will be interested in the promised subtle clues as to the killerís identity.